1. Field of the Invention
This invention relates to a prosthesis inserter which is particularly, although not exclusively, applicable for use for inserting a femoral stem prosthesis.
2. Description of the Prior Art
It is difficult, when inserting certain types of prosthesis into a bone cavity, to judge the position and depth of the prosthesis in the bone and this is particularly so when inserting a femoral prosthesis of the collarless type.
When a femoral stem prosthesis is inserted into the cement in the prepared socket in the femur it is essential to maintain pressure on the cement while it sets. It is also essential that the stem be seated in the intended position according to alignment and depth. To maintain pressure on the cement, a collarless stem requires a temporary proximal seal.
There are many kinds of prosthesis inserters but, in general, they are used to grip the prosthesis to assist the surgeon in implanting it into the prepared opening.
It is particularly difficult to grip the femoral component of a total hip prosthesis without damaging the stem. Damage to a femoral component in the region of the neck may lead to a reduction in the fatigue life of the component since the damage may lead to the initiation of cracks. Furthermore, damage to the spigot or trunion of a modular design, that is a stem component in which heads of different sizes or shapes can be fitted to a spigot, may lead to problems with the engagement of the prosthetic femoral head on the stem. Consequently there are many designs of stem introducing instruments which employ protection of the spigot and the neck of the stem.
It has also been found with earlier designs which clamp only the spigot, that although the inserter may be tightly clamped to the spigot, there can be rotary movement. The rotary movement can be a nuisance during insertion and can result in an incorrect and misaligned insertion.
In many cases it has been found necessary to include a feature on the stem, such as a dimple or a depression into which the stem introducing instrument engages to provide a secure attachment of the stem to the introducer. With such a design of stem introducing instrument, it is usual to achieve engagement onto the stem by advancing an attachment element which engages with the stem. In previous designs the method of advancement has required the surgeon to use two hands to advance the attachment element to secure the stem and, more importantly, has required two hands to be used to effect release. The use of two hands is indicative of the complexity of the methods of engagement and, for a cemented stem, the action to disengage the stem introducing instrument may lead to a disruption of the partially cured cement mantle which may impair the long term result of the implantation. It is therefore desirable to achieve a design of prosthesis inserter which enables the stem to be released with one hand with the minimum disturbance to the cement mantle.